The present invention in general relates to an apparatus and method for controlling a synchronous motor. More particularly, this invention relates to an apparatus and method for controlling a synchronous motor having a magnet is buried in a rotor.
Various control methods related to a synchronous motor in which a permanent magnet is attached to the surface of the rotor (hereinbelow, called an SPM motor) and a synchronous motor in which a permanent magnet is buried in the rotor (hereinbelow, called an IPM motor), for driving the motor without providing a sensor for sensing a rotation position of the rotor are conventionally provided. For example, in (a) Japanese Patent Office Application Laid-Open No. 8-308286, (b) Japanese Patent Office Application Laid-Open No. 9-191698, and the like, a magnetic pole position is estimated on the basis of an error between an estimated current and an actual current, and a vector control of the synchronous motor is performed by using the result of estimation. Furthermore, (c) The Transactions of The Institute of Electrical Engineers of Japan, Vol. 111-D, No. 8, 1991, pp. 639-644 discloses a simple and easy voltage instruction operating method and a simple and easy primary angular frequency setting method in an SPM motor.
The method of (c) will be described in detail hereinbelow. It is additionally written that the xcex3-xcex4 axis of (c) is opposite to that used in the present invention (the xcex3 axis of (c) corresponds to the xcex4 axis of the invention, and the xcex4 axis of (c) corresponds to the xcex3 axis of the invention).
FIG. 6 is a diagram showing the configuration of a conventional control system disclosed in (c).
synchronous motor controlling apparatus comprises following components. That is, an SPM motor 1, and an inverter 2 which applies a PWM modulated sine wave voltage to the SPM motor. A PWM control circuit 3 generates an ON/OFF signal which has been subjected to PWM to a switch in the inverter 2. A current detector 4 detects current flowing from the inverter 2 to the SPM motor 1. A current converter 5 converts the value of the current detected by the current detector 4 to a xcex3-xcex4 axis assumed on the rotor. A microprocessor 6 receives the value of the current detected by the current detector 5, calculates a voltage instruction and a primary angular frequency as described in detail below, coordinate converts the voltage, and outputs the resultant to the PWM control circuit 3.
The microprocessor 6 calculates the voltage instruction based on the following equations (1) and (2).
Vxcex3=R1xc2x7Ixcex3+w1xc2x7xcex1xcex4xe2x88x92w1xc2x7xcexxcex4estxe2x80x83xe2x80x83(1)
Vxcex4=R1xc2x7Ixcex4xe2x88x92Kxcex4xc2x7xcexxcex4estxe2x80x83xe2x80x83(2)
In these equations, R1 denotes primary resistance, w1 is a primary angular frequency, Kxcex4 is a gain (constant), and xcex1xcex4 is a xcex4-axis component of a primary flux linkage. xcexxcex4est is expressed by the equation (3).
xcexxcex4est=L1xc2x7(Ixcex4xe2x88x92Ixcex32/2I0+I0xe2x88x92Ixcex4*)xe2x80x83xe2x80x83(3)
In this equation, L1 denotes an inductance of a primary winding, and I0 is obtained by dividing a flux linkage xcex90 by a magnet by L1. That is, I0=xcex90/L1. Ixcex4* is obtained by multiplying a primary flux linkage instruction xcex9xcex4* by L1. That is, Ixcex4*=xcex9xcex4*/L1.
The primary angular frequency w1 can be calculated using the following equation (4).
w1=w1*xe2x88x92Kmxc2x7Ixcex3xe2x80x83xe2x80x83(4)
In this equation, w1* is an angular velocity instruction and Km is a constant of proportionality.
In the conventional methods (a) and (b), however, the velocity is estimated and the vector control is performed. Consequently, gain adjustment of a velocity control system according to the inertia of a load connected to a motor shaft is necessary, and the computation is relatively complicated. In the conventional method (c), the gain setting due to the inertia of the load is unnecessary and the computation amount is small. However, the method (c) relates to the system of the SPM motor and cannot be applied to an IPM motor having different inductances Ld and Lq on a d-q axis fixed to a stator axis and a different torque generating method.
It is an object of the invention to obtain a control method which can be applied to an IPM motor, in which number of calculations is small, and which does not need gain adjustment according to the inertia of a load.
In order to perform a smooth start without a sensor, accurate primary resistance is necessary, so that another object of the invention is to realize a smooth start by obtaining accurate primary resistance in a short time at the time of starting.